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OFFICE REPORT SACRAMENTO RIVER FLOOD CONTROL PROJECT COLUSA TROUGH DRAINAGE CANAL CALIFORNIA
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US Army Corps of Engineers Sacramento District
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MARCH 1993
20081029157
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DEFENSE TECHNICAL INFORMATION CENTER
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OFFICE REPORT
SACRAMENTO RIVER FLOOD CONTROL PROJECT COLUSA TROUGH DRAINAGE CANAL CALIFORNIA
March 1993
EXECUTIVE SUMMARY
The Water Resources Development Act of 17 November 1986 authorized remedial construction
necessary to restore the Sacramento River Flood Control Project levees along the Colusa Trough Drainage
Canal and the Knights Landing Ridge Cut, subject to review and comment of the project work by the
Secretary of the Army and the submittal of report findings to Congress. The Act stated that if the
Secretary did not comment before the end of a 3-year period beginning on the date of the Act, the project
work would be deemed to have been approved by the Secretary.
Construction General funds were appropriated in FY 90 under the Sacramento River Flood Control
Project to initiate advanced engineering and design studies for the project levees within the study area.
Additional funds were made available in FY 91 and FY 92 to determine the extent and scope of
reconstruction work required to restore the levees to the congressionally authorized and approved design
levels.
The study area includes about 13 miles of project levees on the Knights Landing Ridge Cut and
about 36 miles of project levee on Colusa Trough Drainage Canal. Engineering and geotechnical
evaluations indicate about 11 miles of levees require remedial construction to correct for stability and
seepage problems inherent in the design and construction of the original project. Although there is always
the question of adequate maintenance by the local agencies, it is concluded that the stability and
seepage problems are the result of internal soil conditions (within the levee embankment and subsurface
foundation) and not inadequate maintenance.
8.5 miles of the reconstruction work (located on the Colusa Trough Drainage Canal levee and the
west levee of the Knights Landing Ridge Cut; see Figure 7) is not economically justified incrementally.
The remainder of the work, 2.5 miles along the east levee of Knights Landing Ridge Cut, appears
economically feasible when combined with reconstruction work proposed in the Mid-Valley Area Initial
Appraisal Report (lAR) for that flood hazard area encompassing the community of Knights Landing. The
first cost of the 2.5 miles of levee reconstruction on Knights Landing Ridge Cut is estimated to be about $2
million.
In addition to the above, there are localized depressed areas of the levee crown that do not have the
minimum congressionally approved 3 feet of freeboard above the design water surface. The depressed
areas of the levee crown are outside the limits of the remedial reconstruction work cited above and are
generally located at railroad and road crossings. It is proposed that the local entities responsible for
levee maintenance in these areas be required to install flood barriers or permanenUy fill such locations
under existing maintenance and operation agreements to insure that the design flood stages can be safely
conveyed within the project levees. This work is also within the financial capabilities of the local sponsor,
The Reclamation Board.
The potentially feasible work (2.5 miles of levee reconstruction along the east levee of the Knights
Landing Ridge Cut) will be considered in conjunction with the Mid-Valley Area levee reconstruction plan.
The purpose of this office report is to present findings regarding work performed under Colusa Trough
remedial construction authority. This office report includes a summary of geotechnical analysis, required
levee reconstruction work, design, costs, and economic evaluation.
Considering Colusa Drain/Knights Landing Ridge Cut work in conjunction with the Mid-Valley Area is
in accord with the recommendations presented in the Sacramento River Flood Control System Evaluation, Mid-Valley Area IAR. The east levee of the Knights Landing Ridge Cut in that report was assumed to
provide the congressionally approved design level of flood protection, but it was recognized that
additional detailed geotechnical studies were being done under the subject investigation. The
construction of all work proposed around an independent flood hazard area as one unit will insure that the
design level of flood protection for that area, including the community of Knights Landing, would be met at
one point in time. Geotechnical and design information developed under the Colusa Trough authority will
be incorporated into the Mid-Valley Area design memorandum. In addition, this will minimize engineering
and institutional efforts since only one Project Cooperation Agreement (PCA), one set of plans and
specifications, and one construction contract would be required for the Knights Landing area.
Other areas shown to be incrementally unjustified will be addressed as part of the Total Systems
Costs and Benefits Evaluation pursuant to instructions regarding WRDA-92 and FY-93 work allowance
instructions, and as elements within Phase IV, Lower Sacramento, or Phase V, Upper Sacramento, of the
Sacramento River Flood Control System Evaluation.
Funds programmed for Colusa Trough after FY 92 are not required. Engineering and design costs
expended in the evaluation of the east levee of the Knights Landing Ridge Cut will be transferred to the
Mid-Valley Area design effort and would be cost shared by the local sponsor. Additional funds would
need to be programmed in subsequent years for the Mid-Valley Area engineering and design effort.
TABLE OF CONTENTS
Page
I. Introduction
a) Study Authority 1
b) Study Purpose and Scope 1
c) Other Studies and Reports 1
II. Study Area Description
a) Study Location 2
b) Area Description 3
c) History of Study Area Project Levees 3
III. Problems
a) General 3
b) Levee Embankment Problems 4
c) Flood Problems 6
IV. Engineering and Design
a) General 6 b) Levee Crown and Design Water Surface Profiles 6
c) Geotechnical Analyses 8
d) Designs 10
e) Hydraulics and Hydrology 11
f) Reconstruction Costs 12
g) Economic Justification 16
V. Conclusions 19
TABLE OF CONTENTS (cont'd)
LIST OF TABLES
Page
1 Knights Landing Ridge Cut and Colusa Trough Drainage Canal,
Public Law 84-99 Work - Costs 5
2 Knights Landing Ridge Cut (West Levee) Construction Costs,
Reconstruction Plan - Costs 13
3 Knights Landing Ridge Cut (East Levee) Construction Costs,
Reconstruction Plan - Costs 14
4 Colusa Trough Drainage Canal Construction Costs, Reconstruction Plan - Costs 15
5 Knights Landing Ridge Cut and Colusa Trough Drainage Canal,
Summary of Permanent and Temporary Right-of-Way, Staging Areas,
and Land Acquisition Costs 17
LIST OF FIGURES
1 Location Map, Colusa Basin
2 Vicinity Map .
3 Levee Crown and Water Surface Profiles, Knights Landing Ridge Cut
4 Levee Crown and Water Surface Profiles, Colusa Trough Drain
5 Levee Crown and Water Surface Profiles, Colusa Trough Drain
6 Levee Crown and Water Surface Profiles, Colusa Trough Drain
7 General Location, Levee Reconstruction
8 Levee Breaching, Potential Flooded Areas
9 Reconstruction Design, Landside Ditch Relocation
10 Reconstruction Design, Landside Berm Construction
11 Reconstruction Design, Landside Berm Construction and Ditch Relocation
I. INTRODUCTION
a) Study Authority - The levees of the Coiusa Trough Drainage Canal and the Knights Landing
Ridge Cut have had significant problems over the years. Their integrity has been maintained by local
entities and supplemented by State and Federal aid, Public Laws 84-99 and 93-288, when applicable.
A reconnaissance report was prepared in July 1981 to support the repair of potential project deficiencies.
Resolution of this request was never finalized. With the passage of the Water Resources Development Act
of 1986, repair of these levees was authorized in Section 830 subject to the provisions of Section 903(a).
The authorization reads:
Subject to Section 903(a) of this Act, the project for flood protection along the
Sacramento River and its tributaries, California, authorized by the Flood Control Act of
1917, is modified to authorize and direct the Secretary to accomplish remedial
construction necessary to restore the project flood control levees along the Coiusa Trough Drainage Canal and the Knights Landing Ridge Cut, in accordance with such
report, at a total cost of $11,000,000, with an estimated first Federal cost of $8,250,000
and an estimated first non-Federal cost of $2,750,000.
Section 903(a) required that, prior to commencing construction, the Secretary of the Army review and
comment on the project and report to Congress. If such comment is not made before the end of the
3-year period beginning on the date of enactment of the Water Resources Development Act, the project
will be considered approved by the Secretary of the Army.
b) Study Purpose and Scope - This study was conducted to evaluate the integrity of the existing
levees of the Coiusa Trough Drainage Canal and Knights Landing Ridge Cut, to determine whether the
levees function as designed; to determine whether the levees have the minimum congressionally
approved 3 feet of freeboard above the design water surface; and, if levee reconstruction is needed, to
determine the economic justification for proceeding with construction. The existing levee embankments of
the Coiusa Trough Drainage Canal and Knights Landing Ridge Cut were constructed based on (1) a
design water surface profile, (2) a discharge associated with the design water surface profile, and (3) a
minimum freeboard requirement above the design water surface profile. In general, the study objective
was to develop reconstruction plans to insure that the project levees could safely pass the design flood
stages.
c) Other Studies and Reports - Detailed explorations, soil testing, and analyses of the levees
and foundations within the project area are described in the following reports:
1) "Basis For Design, Levee Construction, Back Levee, RD 108, Sycamore Slough to SPRR
Bridge, Sacramento River Flood Control Project," Corps of Engineers, September 1955.
2) "Design Memorandum No. 2, Sacramento River Flood Control Project, California, Back
Levees of Reclamation District No. 108, Levee Construction General Design," Corps of Engineers,
August 1957.
-1-
3) "Design Memorandum No. 3, Sacramento River Flood Control Project, California, Back
Levees of Reclamation District 108, Levee Construction General Design," Corps of Engineers, August
1957.
4) "Colusa Basin Drainage Canal Levee, Engineering Study," Converse Ward Davis Dixon Inc.,
March 1981.
5) "Office Report, Sacramento River Flood Control Project, California, Engineering and
Economic Evaluation, Colusa Basin Drain and Knights Landing Ridge Cut, Units 127 and 132, Colusa and
Yolo Counties, California," Corps of Engineers, April 1986.
6) "Decision Document, Sacramento River Flood Control Project, California, Engineering and
Economic Evaluation, Colusa Basin Drain and Knights Landing Ridge Cut, Units 132 and 127, Colusa and
Yolo Counties," Corps of Engineers, May 1988.
7) "Geotechnical Assessment of Levees in the Mid-Valley Area, Sacramento River Flood
Control System Evaluation," Corps of Engineers, December 1989.
8) "Plan of Action, Sacramento River Flood Control Project, Colusa Basin Drain and Knights
Landing Ridge Cut," Corps of Engineers, February 1990.
9) "Colusa Basin Appraisal," State of California, The Resources Agency, Department of Water
Resources, May 1990.
10) "Sacramento River Flood Control System Evaluation, Mid-Valley Area, Initial Appraisal
Report," Corps of Engineers, December 1991
11) "Cultural Resources Inventory for the Colusa Basin/Knights Landing Ridge Cut Levees
Project, Colusa and Yolo Counties, California," PAR Environmental Services, April 1992.
12) "Baseline Resources Inventory, Colusa Basin and Knights Landing Ridge Cut," Beak
Consultants Incorporated, May 1992.
II. STUDY AREA DESCRIPTION
a) Study Location - The Colusa Basin is an area northwest of the city of Sacramento. The basin
extends from the Sacramento River on the east to the crest of the foothills on the west, with Stony Creek
and Cache Creek the approximate northern and southern boundaries, respectively. (See Figure 1.) The
basin has a drainage area of approximately 1,700 square miles, a length of about 70 miles, and a
maximum width of about 25 miles. The lands of the basin are used primarily for agriculture, with about
100,000 acres devoted to rice production. Waterfowl hunting at private clubs and on public preserves is
also a major industry in the northern part of the basin. The population of Colusa Basin is mostly contained
within the cities and towns of Willows, Maxwell, Colusa, Williams, Arbuckle, Dunnigan, and Knights
Landing; smaller communities are in the outlying areas. The population of Colusa Basin is increasing at a
rate of about 1.4 percent annually. The January 1987 population estimate was 21,800.
b) Area Description - The development of Colusa Basin into a productive agricultural area has
depended upon the progressive reclamation of the area to prevent flooding, improve drainage, and
provide irrigation. Individuals, local districts, the State, and Federal agencies through the years have
constructed various flood control works necessary to the farming of the fertile areas located within the
basin. Local reclamation districts were the first agencies to develop the area for agriculture.
Investigations and proposals by State and Federal Governments in the early 1900's concerning flood
protection of the Sacramento Valley greatly influenced the subsequent developments within the basin.
c) History of Study Area Project Levees - The levee of Reclamation Districts 108 and 787 and
Maintenance Area 12 extends from the vicinity of Colusa along the eastern side of the Colusa Trough
Drainage Canal through Knights Landing. (See Figure 2.) This levee was originally constructed to
protect lands to the east of the Colusa Trough Drainage Canal from flood runoff originating from the
western foothills. Local interests constructed the Colusa Trough Drainage Canal, which flows south from
its junction with Willow Creek above the town of Colusa and then along the alignments of the levee of
Reclamation Districts 108 and 787. Excavated material was used to build the levee of this channel, and in
some reaches excavation was necessary to provide a continuous drainage channel of the desired
capacity. The levee was originally constructed by local interests between 1911 and 1918 using a
clamshell dredge. The levee was gradually improved and final modifications were completed in 1958 to
meet the design specifications for the Sacramento River Flocd Control Project and to provide flood
protection for lands to the east against flows up to 20,000 cubic feet per second (cfs). However,
floodflows that exceed the Trough's in-channel capacity of 1,500 cfs have caused and will continue to
cause extensive flooding of lands west of the levee.
During low stages on the river, flows from the Colusa Trougr. Drainage Canal are discharged through a
concrete structure, the Knights Landing Outfall Gates, into the Sacramento River. When the stage of the
Sacramento River is high, the gates are closed, and flows frcrn Colusa Trough Drainage Canal are
conveyed through Knights Landing Ridge Cut into the Yolo Bypass. The Knights Landing Ridge Cut, which
has a bottom width of 400 feet, was constructed by excavating two parallel channels and using the
excavated material to construct two levees on the outside of each channel. The leveed cut was designed
to convey 20,000 cfs. The two combined excavated channels act as low flow outlet channels for the
Colusa Trough Drainage Canal.
III. PROBLEMS
a) General - The levees in the Colusa Trough Drainage Canal and Knights Landing Ridge Cut
have experienced subsidence, slippage, and partial collapse over the years. Historic records, dating to
1915, indicate failures have occurred on both sides of the levees and repairs have been made throughout
their existence. Records dating to 1959 show subsidence and slumping of many short levee reaches (200
feet or less). In some cases, levees were repaired by excavating and recompacting as much as one-half
-3-
of the levee cross section. These failures have been extensive and threaten the integrity of the levee
system.
The cost of such work has frequently exceeded the financial capabilities of the local districts to repair the
levees, and the assistance of the Corps of Engineers has been provided under Public Law 84-99.
Previous Public Law 84-99 work is shown in Table 1. However, continuous intensive maintenance
programs and prompt and effective emergency actions have been necessary to prevent levee breaches
and flooding of the protected areas.
b) Levee Embankment Problems - Corps documents dating to 1951 have described levee
deformation, slippage, and partial collapse. Levee damage has resulted from the following: (1) loss of
strength and cracking of the near surface soils, (2) precipitation and flood stage water forces, (3) a weak
layer of foundation clay and/or organic material, and (4) over steepened levee geometry. Many of the
failures have been on the landside of the levees. Slope failures are often shallow surficial slides involving
the upper 5 feet or so of material and do not extend into the crown. Deeper slides manifest themselves as
longitudinal cracks extending into the crown. The landside or waterside slope gradually deforms several
inches to several feet per day until equilibrium of the sliding mass is reached. The typical result is a 4- to
7-foot vertical escarpment in the crown which may extend for 200 to 1,000 feet. Material in the levee
foundation moves laterally along a weak layer of soft clay and organic debris (tule reeds, grasses, carbon
chunks, and decayed matter) and comes to rest 20 to 30 feet beyond the levee toe. Deformation
problems have been described as several feet of subsidence in the crown accompanied by bulging of the
sides between the toe and crown.
During 8 of the past 34 years (1958, 1959, 1969, 1974, 1975, 1980, 1983, and 1986), damages to the
levees of the Colusa Trough Drainage Canal, RD 108/787, warranted Public Law 84-99 assistance.
Repairs in 1959 consisted of reconstructing small portions of the levees at various locations. In 1974,
1980, and 1984 (1983 damages), repairs consisted of reconstructing approximately 5,200 feet of the levee.
During the same 34-year period, Knights Landing Ridge Cut levees required assistance under Public Law
84-99 in 4 years (1956,1963, 1975, and 1986). In 1963, repairs consisted of reconstructing approximately
1,600 feet of levees on both sides of the channel. In addition, in 1983 non-Federal interests received
assistance from the Federal Emergency Management Agency for damages not subject to Public Law
84-99 assistance.
Repairs have included removal and compaction of the failed material to flatten slopes with the inclusion of
a berm to counterbalance tbe rotational failure of the levee fill. A total of 67 levee repair and
reconstruction sites have been noted in Corps documents since 1956. In many other instances,
non-Federal interests have repaired the levees when Federal aid was not available as levee failures
occurred in years when no flood emergency was declared.
TABLE 1 KNIGHTS LANDING RIDGE CUT AND COLUSA TROUGH DRAINAGE CANAL
PUBLIC LAW 84-99 WORK
Year Reclamation District
Levee Mile Length Damage Actual Cost (S) Cost ($) Oct91
Price Level
1956 KLRC 2.5 1,600 Slip, Subsidence
50,000 290,358
1963 KLRC 0.7, 0.85 1,850 Slip, Subsidence
60,000 300,344
1969 108 787
2.4 Combined 350
Slip 22,000 88,808
1974 108 0.0,2.1-3.7 Combined Structural Combined 787 2.2, 4.2 2,250 Failure 69,000 191,380
1975 108 14.9, 15.4 400 Landside Slip 37,000 86,975 787 1.98, 2.73 200 Slip 23,500 55,241
1980 108 0.15, 1.8,2.25 3,150 Slip, Subsidence
304,000 466,470
1983 108 0.22-17.4 10,300 Slips 509,000 618,557
1986 KLRC 2.25, 2.4, 2.6 900 Slip, Subsidence
TOTAL COST
60,000 70,110
1,134,500 2,168,243
KLRC = Knights Landing Ridge Cut
5-
c) Rood Problems - Under existing conditions, land on the west side of the Colusa Trough
Drainage Canal levee is flooded during peak floodflows. This situation has existed since the early part of
the century when the levee was first constructed by non-Federal interests. During an event such as the
100-year (1983) flood, the peak flood stage would be reduced about 3 feet by a levee breach. Peak
stages are of short duration when compared with periods of inundation generally experienced by the
westside lands (peak stage periods generally last about 1 to 2 weeks on the average). The primary
problem is that flow in the Yolo Bypass produces prolonged periods of backwater inundation in the Colusa
Trough Drainage Canal. Flood records indicate that westside lands may be inundated for several months
and that the inundation may extend into May.
If levees along the Colusa Trough Drainage Canal are breached, there will be a reduction in the extent of
westside lands inundated. This reduction in flooded areas around the perimeter is not really significant.
The duration of flooding of the westside lands would also change because of a levee break but is
dependent on how floodwaters are removed from flooded areas east of the Colusa Trough and
reintroduced into the system. There will be no change to westside flooding levels, assuming the Colusa
Trough Drainage Canal levee provides the design level of protection.
Flood stages in the Colusa Trough Drainage Canal and Knights Landing Ridge Cut are a function of runoff
upstream from the town of Colusa, local runoff, and backwater effects from the Yolo Bypass. Antecedent
weather conditions prior to floods are characterized by extensive and frequent rainy periods. During these
periods, rainfall which averages more than one-third of an inch per day occurs more than 50 percent of
the time, with only shea periods of clearing (less than 10 days) for periods up to 4 months. These wet
weather conditions result in saturation of the levees and corresponding softening of the levee fill adjacent
to cracks or fissure surfaces. As noted in the geotechnical analyses (Section IV-c), the fissure orientation,
intrusion of water, and associated softening of the fissure surfaces may cause slope failures.
Levee damages usually consist of partial slope failures or subsidence, with the majority of damages
occurring on the landward side of the levee. Repair of these damages often requires excavation and
reconstruction of the entire levee cross section. During reconstruction it has been observed that the
levees contain fissured clay and that the underlying foundation contains organic clays with local layers of
vegetation that has not decomposed.
IV. ENGINEERING AND DESIGN
a) General - This study was conducted to evaluate the integrity of the existing project levees of
the Colusa Trough Drainage Canal and Knights Landing Ridge Cut; to determine whether the levees
function as designed; to determine whether the levees have the minimum congressionally approved 3 feet
of freeboard above the design water surface; and, if levee reconstruction is needed, to determine the
economic justification for proceeding with reconstruction. If levee reconstruction is needed, reconstruction
plans would be developed to insure that the project levees can safely pass the design flood stages.
b) Levee Crown and Design Water Surface Profiles - Levee crown surveys were completed on
the Colusa Trough Drainage Canal and the Knights Landing Ridge Cut in September and December of
-6-
1990, respectively. Levee crown elevations are referenced to mean sea level datum. Levee crown
stationing (and the design water surface profile) was based on "Levee and Channel Profiles," Corps of
Engineers, March 1957, as revised.
Survey points were taken on the centerline of the levee crown about every 1,000 feet and at breaks in the
levee crown profile. Additional survey points were taken at railroad crossings, road crossings, and at
other significant physical features. Levee crown profiles developed from the survey data are shown in
Figures 3 through 6.
The profile plots indicate the non-uniformity in the levee crown surfaces in the study area. In addition, the
plots indicate that some road crossings cut through the levee embankments at elevations 1 to 3 feet
below the adjacent levee crown elevations.
Design water surface profiles were developed for Colusa Trough Drainage Canal and Knights Landing
Ridge Cut as part of the Sacramento River Flood Control Project, as indicated by "Levees and Channel
Profiles," Corps of Engineers, March 1957. Design water surface elevations were based on a specified
design discharge (no recurrence interval or frequency was attached to that design discharge) and adopted concurrent conditions at the confluences of study area streams and bypasses.
Project flood plains were originally adopted by the March 1917 Flood Control Act as taken from House
Document No. 81,1st Session, dated 1910. In 1923 , House Document No. 81 was modified to show
changes to the recommended project because of significant cost increases, local desires, and to
incorporate work which had already been done by locals in the interim. Revised values for project design
flows and flood plains were established and included in the report "Flood Control in the Sacramento and
San Joaquin Basins," printed as Senate Document No. 23, 69th congress, 1st Session, 1926. This is the
basic document authorizing the 1928 revision of the project. Since 1928, project design flows and water
surface profiles have been reevaluated and modified based on available hydrologic information and more
detailed hydraulic studies, and as various segments of the project were constructed. These revisions
have been agreed to by The Reclamation Board, State of California, and the Corps of Engineers and
published as "Levee and Channel Profiles, Sacramento River Flood Control Project," 15 March 1957.
The agreed-to 1957 design water surface profiles are shown on Figures 3 through 6 and can be compared
to the levee crown profile plots.
Three feet is the minimum freeboard on the Colusa Trough Drainage Canal and Knights Landing Ridge Cut
project levees to meet design requirements for the flood control project levees and to provide for a uniform
level of protection from overtopping. An inspection of the profile plots indicates that freeboard is
inadequate on Knights Landing Ridge Cut at the Road 16 crossing and in the vicinity of channel mile 12,
and on Colusa Trough Drainage Canal at the Road 99E crossing, in the vicinity of channel mile 4, between
channel miles 12 and 14, at the County Line Road crossing, and in the vicinity of channel mile 17.
Although road crossings do not meet minimum design freeboard requirements, local levee maintaining
agencies should have operational procedures for sandbagging or for installing flood gates at these
locations during high flood stages. In addition, other localized depressed areas of the levee crown have
deficient freeboard ranging up to about a maximum of 1 foot. Because these areas are very localized,
because the magnitude of the freeboard deficiency is small, and because the reasons for the deficiencies
cannot be positively associated with design or construction deficiencies, the depressed areas should be
raised under existing maintenance and operation agreements.
c) Geotechnical Analyses - Geotechnical analyses were conducted on the Colusa Trough
Drainage Canal and Knights Landing Ridge Cut project levee embankments and levee foundations to
evaluate levee stability and provide reconstruction designs for levees with inherent design and
construction deficiencies. Reconstruction designs were selected on the basis of current explorations and
testing and a review of previous investigations and information.
The current geotechnical investigation included a total of 88 borings drilled in June and July of 1990 for
the purpose of determining the properties and characteristics of the levee embankment and foundation
soils. A 6-inch diameter hollow-stem auger was used to drill to depths of 40 feet from the levee crown
and 20 feet from the levee toe (generally two borings per site). Additional borings were drilled to
investigate slumping. Standard penetration tests (SPT's) were conducted continuously from the surface to
a depth of 20 feet and then at 5-foot intervals thereafter except in alternating borings where undisturbed
and bulk samples were taken. In addition, in November 1990, a total of five exploration trenches were
excavated in the levee embankment at selected sites within the project area for the purpose of evaluating
levee crackage. Two trenches were excavated on the landside of the Knights Landing Ridge Cut, and 3
trenches were excavated along the Colusa Trough Drainage Canal levee at known levee problem areas.
The purpose of the trenches was to trace the depth of the larger cracks and to view the zone of drying and
cracking. The above information was supplemented with boring logs from previous investigations by the
Corps of Engineers, other geotechnical firms, and with data from past levee repairs.
Levee embankment cross section surveys indicated levee slopes ranging from 1.5 horizontal to 1 vertical
(1.5H:1V) to 4.0H:1Von the waterside and 2.0H:lVto 5.5H:1V on the landside. The crown width varies
from 12 to 60 feet on the Knights Landing Ridge Cut and 18 to 80 feet on the Colusa Trough Drainage
Canal. The predominant crown width is 25 feet for the Colusa Trough Drainage Canal and 15 feet for the
Knights Landing Ridge Cut. The typical levee height above the natural ground surface is 15 feet for the
levee reaches. However, the levee in some reaches is as high as 20 feet. A landside ditch 10 feet deep
and 30 feet wide parallels the landside toe for much of the project.
The laboratory testing program indicated that the soil samples obtained from the levee embankments and
foundations were primarily clays. There were 15 samples selected to represent the embankment and
foundation and 8 samples chosen as representative of the clay-organic layer. Testing indicated that a
well defined peak strength was not reached by 10 of the 23 samples tested. The descriptions of past
failures indicated a gradual remolding and loss of strength of material prior to failure; however, creep as a
mode of failure was not established.
Soil-lime testing consisted of using matenal from three sites that were selected as representative of the
levee embankment and foundation soils. Clay-organic material was not tested because acid from
decaying organic matter inhibits the interaction of lime with clay. Soils with an organic content greater
than 20 percent are considered nonreactive with lime. Soils tested had an organic content of about 6
percent. Laboratory test results indicated that cracking and shallow sloughing may be prevented with the
addition of 4 percent lime to the clay and that the soils of the project levees are conducive to lime
treatment. Potential reconstruction work on the Colusa Trough Drainage Canal, about 8,000 lineal feet of
levee between roads 99E and 98A, would use a lime treatment to prevent cracking of the near-surface
levee material. Lime at a rate of 4 percent by weight would be mixed in place to a depth of 2 to 3 feet.
Any organic matter encountered would be removed.
The slope stability analyses determined that the critical condition for landside slope stability occurs at the design flood stage with uplift pressure transmitted through trie shallow foundation organic layer. Waterside
slope stability is most critical at low-flow conditions at locations where the freeboard is greatest.
All levee reaches have shallow stability problems regardless of slope geometry or flood stage. The
expansion characteristics of the clay materials and the long periods of seasonal wetting and drying result
in progressive loss of strength. The shallow slides are confined to the upper few feet of material and
typically daylight at the levee toe, channel bank, or ditch bank. Deeper slides fall along the plane of the
clay-organic layer. In general, the more stable reaches have (1) slopes flatter than 3H:1 V, (2) a landside
height less than 15 feet, (3) no channel or ditch bank within 50 feet of the levee toe, and (4) no underlying
clay-organic layer. The analyses did not consider the dense growth of large trees along the waterside
bank of the Colusa Trough Drainage Canal. Based on the height of these trees, the root system is
estimated to extend to a depth of 30 feet into the foundation soil. The roots could increase the resistive
force of the available shear strength along the failure plane.
Based on the results of the geotechnical evaluation, engineering judgement, and past performance, the
following reconstruction plans are recommended to insure that the project levees can safely convey the
design flood stages:
Colusa Trough Drainage Canal *
15,500 lineal feet landside irrigation ditch relocation and intermittent toe berm construction
(with 8,000 lineal feet of lime treatment) up to Road 98A. Upstream of Road 98A plan consists
of 29,000 lineal feet of landside irrigation ditch relocation and toe berm construction.
Knights Landing Ridge Cut *
West Levee - Reconstruction plan consists of 500 lineal feet of landside irrigation ditch
relocation.
East Levee - Reconstruction plan consists of 13,500 lineal feet of landside irrigation ditch
relocation and 11,500 lineal feet of toe berm construction.
* See Figure 7
9-
d) Designs - Designs for reconstruction of levees along the Colusa Trough Drainage Canal and
Knights Landing Ridge Cut were based on results from the current geotechnical analyses and a review of
test results and previous designs presented in "Colusa Basin Drainage Canal, Engineering Study"
(reference 4).
The test results presented in the consultant's report indicated that the fissured structure of the uppermost
foundation material significantly affects the strength of the material. The stability analysis showed that
failure surfaces passing through this fissured layer could cause the Colusa Trough Drainage Canal levee
to fail. Thus, the presence of this fissured layer suggests that the levee should be reshaped. The report
indicates the following three solutions (reconstruction designs) based on their testing results:
1) Reconstruction design 1 - The levee would be excavated to foundation level and then reconstructed. The results of a number of soils tests indicated that excavating the levee to the
foundation material and recompacting the soil such that the fissured structure is eliminated would be a
viable solution. Previous repairs of the levee used this method with the provision that highly organic
layers of materials be removed and inspections made to insure that such layers were not present when the
levee was replaced. Most of the repaired sections have been performing satisfactorily; however, a
previously repaired section in RD 108 reportedly failed. The failure could be due to inadequate depth of
excavation or width of the key (remolding of fissured clay).
2) Reconstruction design 2 - The driving force would be reduced by removing material from the top
of the slope and placing it near the toe. This measure involves excavating a portion of the landside slope
and decreasing the crest width and placing and compacting the excess material into a berm near the toe
of the slope. The geometric configuration would be a 16-foot crown width with a 2H:1V landside slope
and a 27-foot wide berm at the landside toe. The waterside slope would remain unchanged. In this
method, the final levee would have a split section, and the factor of safety would be higher due to an
improved geometric configuration. This plan would not remove the fissured structure or organic layers in
the unexcavated portions of the levees.
3) Reconstruction design 3 - The basic designs of the first two alternatives would be used. This
•design consists of excavating the levee and the upper few feet of foundation soils and compacting the
material into the split-level geometric configuration described in design 2. This method would give the
highest factor of safety.
Based on analysis of the designs presented in the consultant's report, geotechnical analyses done for the
current investigation, and basic engineering judgement, the following designs have been recommended:
a) Berms will be added to provide a differential of 15 feet between the levee crest and the top
of berm to stabilize the levee slope from potential deep failures. The berm is to extend horizontally a
minimum of 20 feet from the levee slope with a minimum thickness of 2 feet. (See Figure 10.) Ditches
are to be relocated a minimum distance of 50 feet from the levee toe . (See Figure 11.)
b) The upper 2 to 3 feet of material from the levee crown to the toe will be treated with lime to
prevent cracking and to stabilize the levee slopes from potential shallow slides and deformation. The
treatment area will extend between roads 99E and 98A.
-10-
c) Landside ditches near the levee toe will be relocated a minimum distance of 50 feet from
the levee toe to improve slope stability. (See Figure 9.)
e) Hydraulics and Hydrology - Within the study area, the Colusa Trough Drainage Canal is
leveed only on the left bank for about 36 miles. The upstream limit of the levee is south of the city of
Colusa and just south of Highway 20. The Knights Landing Ridge Cut is leveed on both the left and right
banks for about 13 miles.
Floodflows accumulating upstream of the project levee on Colusa Trough Drainage Canal are conveyed
downstream past Highway 20 and down the drain to the Knights Landing Ridge Cut. Additional local
inflows are intercepted at various points along the drain. During low stages, flows do not enter the
Knights Landing Ridge Cut but are discharged through the outfall gates into the Sacramento River just
north of the community of Knights Landing. During high stages, the outfall gates are closed and
floodflows are conveyed through the Knights Landing Ridge Cut into the Yolo Bypass.
The study area has a gaging station at Highway 20 (flow and stage) and at Knights Landing (stage only).
The gage at Knights Landing is upstream of the entrance to the Knights Landing Ridge Cut and west of the outfall gates to the Sacramento River.
The Corps of Engineers modified the levee embankments of the Knights Landing Ridge Cut in 1952 and
the Colusa Trough Drainage Canal in 1956 and 1958 to meet design criteria authorized for the Sacramento
River Flood Control Project. The minimum design freeboard was specified as 3 feet. The approved
design water surface profiles are shown on Figures 3 through 6. Since modification of the existing levees
by the Corps, no breaching of the levee embankments has occurred to date, although areas of significant
levee distress have been observed (see photo, front cover) during and after flood events.
A design overflow location exists immediately upstream of the entrance to the Knights Landing Ridge Cut
on the right bank. Overflow is initiated at about the design water surface elevation at this location. If
overflow occurs, excess flows would be conveyed around the project levee and downstream on the
landward side of the west levee of the Knights Landing Ridge Cut.
During the 1986 flood event, overflow did not occur to the west of the Knights Landing Ridge Cut for an
observed peak flood stage of 35.94 feet (msl datum) at Knights Landing (see 1986 high water mark profile
of Figure 3). During the 1983 flood event, when the observed peak flood stage was 37.35 feet at this
same location, overflow did occur and floodflows traveled southerly along the landward side of the west
levee of the Knights Landing Ridge Cut.
The peak stage for the 1986 flood in the Yolo Bypass at the confluence with the Knights Landing Ridge Cut
was about 34.0 feet. (See Figure 3.) The peak stage exceeded the design water surface by about 0.3
feet. Based on the following stage-frequency data, which was developed for Yolo Bypass at this location
(Yolo Bypass at the confluence with Knights Landing Ridge Cut), the peak stage represented a recurrence
interval of 50 to 55 years.
-11-
Recurrence interval (years) 50 40 30 20 10
Yolo Bypass stage (feet) ** 33.7 33.1 32.7 32.0 30.4
** Yolo Bypass at the confluence with Knights Landing Ridge Cut
For the 1983 flood, the peak flow rate observed at Highway 20 was 15,700 cfs. According to the
Department of Water Resources (State of California), the 1983 recorded flow did not include overbank flow. Total flow has been estimated as 22,400 cfs. Using the following discharge-frequency data
supplied by Hydrology Section, the 1983 peak flow, 22,400 cfs, at this location corresponds to a
recurrence interval of about 40 years. The peak flow rate for the 1986 flood was 11,600 cfs and
corresponds to a recurrence interval of about 10 years.
Recurrence interval (years) 100 50 25 10
Peak flow (cfs) ** 34500 26000 19000 11800
** Colusa Trough Drainage Canal at Highway 20
Since peak flood stages in the Knights Landing Ridge Cut and Colusa Trough Drainage Canal are
influenced by the flood stages in Yolo Bypass (backwater condition), a one-dimensional unsteady flow
model was developed for the study area. Water surface profiles were developed for various flow rates
and downstream stage-boundary conditions. The maximum peak flood stages during the 1983 and 1986
floods were estimated to have recurrence intervals of 40 to 55 years based on the hydraulic modeling and
hydrologic inputs.
f) Reconstruction Costs - Since previous studies have never identified an economically feasible
project for the subject study area, costs in the current investigation were only developed to that extent
necessary to determine whether the work was potentially feasible.
•The geotechnical evaluations, limits of reconstruction, reconstruction designs, costs of levee
modifications and drainage facilities, and costs of relocations were done to that detail necessary for
incorporation into a design memorandum. This was done such that if the reconstruction was shown to be
infeasible, the information would be available to local entities and would permit those entities to make
decisions and implement the necessary work without significant additional engineering and design efforts.
The reconstruction costs were developed for three separate reconstruction plans, the west levee of the
Knights Landing Ridge Cut, the east levee of the Knights Landing Ridge Cut, and the levee on the Colusa
Trough Drainage Canal. Each of these plans was associated with a potential flood hazard area (see
Figure 8 for the general location of the flood hazard areas) for economic purposes.
Reconstruction costs are shown for each plan in Tables 2, 3, and 4. A general description of each
applicable plan is contained in the first footnote of each table. Costs for relocations, levee modifications
and drainage facilities were done in sufficient detail for incorporation into a design memorandum. Costs
for real estate were estimated based on work previously accomplished by Real Estate Division for the
Mid-Valley Area cost estimates, which include similar land types for value purposes. This work was
12-
TABLE 2 KNIGHTS LANDING RIDGE CUT (WEST LEVEE)^
CONSTRUCTION COSTS RECONSTRUCTION PLAN
Item First Cost
Lands and Damages $50,000 2/
Relocations $33,000
Fish and Wildlife Facilities $20,000 2/
Levee Modifications and Drainage Facilities $76,000
Cultural Resources Preservation $5,000 2/
Planning, Engineering, and Design $190,000 ZJ It
Construction Management $10,000 2/
TOTAL $384,000
1/ Reconstruction plan consists of 500 lineal feet of landside irrigation ditch relocation.
li Estimated using amounts for similar work shown in the Sacramento River Flood Control System Evaluation - Initial Appraisal Report - Mid-Valley Area, December 1991.
h Includes costs expended during current investigation.
-13-
TABLE 3 KNIGHTS LANDING RIDGE CUT (EAST LEVEE)17
CONSTRUCTION COSTS RECONSTRUCTION PLAN
Item First Cost
Lands and Damages $400,000 2/
Relocations $78,000
Fish and Wildlife Facilities $200,000 ll
Levee Modifications and Drainage Facilities $803,000
Cultural Resources Preservation $20,000 ll
Planning, Engineering, and Design $400,000 %l h
Construction Management $70,000 li
TOTAL $1,971,000
y Reconstruction plan consists of 13,500 lineal feet of landside irrigation ditch relocation and 11,500 lineal feet of toe berm construction.
h Estimated using amounts for similar work shown in the Sacramento River Flood Control System Evaluation - Initial Appraisal Report - Mid-Valley Area, December 1991.
h Includes costs expended during current investigation.
14-
TABLE 4 COLUSA TROUGH DRAINAGE CANAL17
CONSTRUCTION COSTS RECONSTRUCTION PLAN
Item First Cost
Lands and Damages $700,000 2/
Relocations $8,000
Fish and Wildlife Facilities $400,000 ll
Levee Modifications and Drainage Facilities $2,664,000
Cultural Resources Preservation $40,000 li
Planning, Engineering, and Design $1,200,000 till
Construction Management $190,000 2/
TOTAL $5,202,000
1/ Reconstruction plan consists of 15,500 lineal feet landside irrigation ditch relocation and intermittent toe berm construction (with 8,000 lineal feet of lime treatment) between Knights Landing and Road 98A. Upstream of Road 98A plan consists of 29,000 lineal feet of landside irrigation ditch relocation and toe berm construction.
li Estimated using amounts for similar work shown in the Sacramento River Flood Control System Evaluation - Initial Appraisal Report - Mid-Valley Area, December 1991.
li Includes costs expended during current investigation.
-15-
coordinated with District Real Estate Division, and a breakdown of cost for each plan is presented in Table
5. Other costs were also estimated using amounts for similar work shown in the Sacramento River Flood
Control System Evaluation, Initial Appraisal Report, Mid-Valley Area, December 1991. Since, as indicated
below in the Economic Justification, the reconstruction work was shown to be infeasible based on existing
conditions and an incremental resource analysis, no further refinement of quantities and cost was
considered necessary.
g) Economic Justification - Based on past performance and the geotechnical evaluation, the
levee reconstruction shown in Figure 7 is necessary to insure that the design flood stages can be safely
conveyed by the project levees. The geotechnical evaluation also indicated a high potential for levee
failure at flood stages equal to or greater than the higher of the peak flood stages that occurred during the
1983 and 1986 floods.
Potential flooded areas (see Figure 8) were developed assuming various breach scenarios and different
without project condition levels of flood protection. Without project damages were computed for the
various scenarios in an effort to determine whether the levee reconstruction was incrementally justified at a
reconnaissance level.
During high flood stages a levee break on the west side of the Knights Landing Ridge Cut (at the site
where ditch relocation is the recommended repair, see Figure 7) would result in flooding to an area
bounded by the Cache Creek and Yolo Bypass project levees. (See Figure 8.) The potential flooded
area is predominantly agriculture with farmsteads. Even if the recommended levee repair is made at this
time, higher levels of flood protection for this area are probably not possible. As indicated previously,
floodwaters circumvented the upstream limit of the west levee of the Knights Landing Ridge Cut during the
1983 flood and caused flood damages to areas landward of that levee. In addition, during the 1983 flood
the north levee of Cache Creek just downstream of the community of Yolo was sandbagged to prevent
overflow of the levee. If overflow or levee breaching would occur at this location, floodwaters would be
conveyed downstream into the same general area shown flooded in Figure 8 (the estimated design level
of flood protection for Cache Creek in the vicinity of Yolo is probably between a 10- and 20-year
recurrence interval). Based on the above, higher levels of flood protection could not be achieved for that
flood hazard area west of the Knights Landing Ridge Cut by relocating the ditch adjacent to the landward
toe of the west levee. Since higher levels of flood protection cannot be attributed to the recommended
repair for the west levee of the Knights Landing Ridge Cut, this work is not economically justified on an
incremental basis.
Although the reconstruction proposed for the west levee of the Knights Landing Ridge Cut cannot be
justified, the local maintaining agency or the State should consider doing the necessary work. If
economic justification were shown and if Federal participation were approved, the cost of relocating ditch
facilities would have been a local responsibility under current cost sharing policies.
-16-
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For the Colusa Trough Drainage Canal, about 8.5 miles of levee reconstruction is proposed just upstream
of the Knights Landing Ridge Cut. (See Figure 7.) Based on the geotechnical and hydraulic analyses,
the most probable levee breach location is in the uppermost levee reach of the recommended repair. If a
levee were to break at an upstream location, another break downstream on Colusa Trough Drainage
Canal is not expected. The potential flooded area for the above condition is shown in Figure 8.
The potential flooded area is bounded by a local levee to the south, the Sacramento River levee to the
east, and the Colusa Trough Drainage Canal levee on the west. The area is predominantly agriculture with
scattered farmsteads. The economic evaluation indicated that the average annual without project
damages for existing conditions, a 21-day duration of flooding, and a 50-year nondamaging level of
flood protection is about $115,000. Even if all the foregoing damages could be eliminated by the
proposed reconstruction, the potential benefits would only support about $1.4 million of repair work. As
shown in Table 4, the cost of levee modifications is in excess of $2 million which would indicate that the
work on Colusa Trough Drainage Canal is economically infeasible on an incremental basis.
In addition to the above, the Sacramento River side of the Colusa Basin has levee reaches with design
levels of flood protection between 30-year and 40-year recurrence intervals. The 1983 peak flood stages
in the Colusa Trough Drainage Canal had estimated recurrence intervals of 40 to 60 years (there were
reaches of observable levee distress during the 1983 flood but no levee failures, although emergency
repairs were subsequently required as indicated in Table 1). Based on past records, infrequent storm
events generally produce high flood stages in the Colusa Trough Drainage Canal at about the same time
as high flood stages are occurring in the Sacramento River opposite the Canal. Because of the above,
higher levels of flood protection for that area east of the Colusa Trough Drainage Canal probably cannot
be achieved by the recommended repairs.
The reconstruction work proposed for the east levee of the Knights Landing Ridge Cut (see Figure 7)
would insure that this project levee could safely convey the design conditions. A levee break at either of
the repair sites shown would inundate an area confined by project levees on all sides. (See Figure 8.) In
the "Mid-Valley Area, Initial Appraisal Report", Corps of Engineers, December 1991, reconstruction work
was also recommended for the west levee of the Sacramento River opposite the community of Knights
Landing. The estimated existing (without project condition) levels of flood protection for the Knights
Landing area were estimated at a 40-year recurrence interval on the Knights Landing Ridge Cut side and
a 60-year recurrence interval on the Sacramento River side.
The average annual without project damages for existing conditions, a 21-day duration of flooding, and a
40-year nondamaging level of flood protection is about $530,000 for the Knights Landing area. The
combined cost of levee repairs for this area is about $3.7 million (the cost of reconstruction of the west
levee of the Sacramento River is about $1.7 million based on the Mid-Valley Area, Initial Appraisal
Report, and the cost of reconstruction of the east levee of the Knights Landing Ridge Cut is about $2
million as shown in Table 3). If half the benefits within the freeboard range are attributed to the
reconstruction proposed, the benefits exceed the costs (a benefit to cost ratio that could range from 1.1 to
-18-
1.5 depending on upstream levee breaching), The cost of doing the combined work could be less than
that shown above if only one contract for construction is necessary (combining the reconstruction work will
minimize engineering and institutional efforts since only one Project Cooperation Agreement, one set of
plans and specifications, and one construction contract would be required for the Knights Landing area).
Based on the economic evaluation (results summarized above), reconstruction work for the levees
surrounding the community of Knights Landing is economically justified based on an incremental analysis
and assuming that the Mid-Valley Area work is combined with this work as one contract. Reconstruction
work for the west levee of the Knights Landing Ridge Cut and the Colusa Trough Drainage Canal is not
justified incrementally
Because public safety is a primary concern, there is also potential justification for Federal participation in
reconstruction work for the levees around Knights Landing. This potential flood hazard area includes
about 500 structures, primarily residences, and about 850 people. A major adverse impact resulting from
a levee failure in this area is the potential for loss of human life. Depths of flooding resulting from levee
failure could range up to a maximum of 15 feet. Because of the depths of flooding possible and the
potential for unexpected levee failures, loss of life could result.
V. CONCLUSIONS
Based on a comparison of with and without project conditions, reconstruction work proposed for the
Colusa Trough Drainage Canal levee and the west levee of the Knights Landing Ridge Cut is not
economically justified incrementally. Reconstruction work proposed for the east levee of the Knights
Landing Ridge Cut is incrementally justified when combined with repairs recommended for the west levee
of the Sacramento River (as presented in the "Mid-Valley Area, Initial Appraisal Report", Corps of
Engineers, December, 1991) opposite Knights Landing.
Further development of plans for reconstruction of the east levee of Knights Landing Ridge Cut will be
accomplished in conjunction with the Mid-Valley Area design effort. The construction of all work
proposed around an independent flood hazard area as one unit will insure that the design level of flood
protection for that area, which includes the community of Knights Landing, will be met at one point in time.
Geotechnical and design information developed under the Colusa Trough Drainage Canal investigation
can easily be incorporated in the Mid-Valley Area design memorandum. In addition, this will minimize engineering and institutional efforts because only one Project Cooperation Agreement, one set of plans
and specifications, and one construction contract would be required for the Knights Landing area.
Reconstruction work which has been shown to be incrementally infeasible in this investigation will be
considered in other phases of the Sacramento River Flood Control System Evaluation. That work
proposed for the Colusa Trough Drainage Canal levee (which is incrementally infeasible) will be
considered along with the west levee of the Sacramento River opposite the canal. These two levees
provide flood protection for the same potential flood hazard area and, as such, it would be appropriate to
19-
evaluate these levees concurrently. Based on the above, repair work for the Colusa Trough Drainage
Canal levee will be addressed in the Initial Appraisal Report for the Upper Sacramento Area, Phase V, of
the Sacramento River Flood Control System Evaluation. This same reasoning also applies to work
proposed for the west levee of the Knights Landing Ridge Cut (which is also incrementally infeasible).
This work will be addressed in the Initial Appraisal Report for Lower Sacramento Area, Phase IV, of the
Sacramento River Flood Control System Evaluation.
-20-
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SACRAMENTO DISTRICT. CORPS OF ENGINEERS SEPTEMBER 1992
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SACRAMENTO DISTRICT. CORPS Of ENGINEERS SEPTEMBER 1992
FIGURE 7
LEVEE BREACHING POTENTIAL FLOODED AREAS
SACRAMENTO DISTRICT. CORPS OF ENGINEERS SEPTEMBER 1992
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FIGURE 11
